首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   170篇
  免费   1篇
  国内免费   3篇
化学   19篇
数学   115篇
物理学   40篇
  2023年   1篇
  2022年   3篇
  2021年   2篇
  2020年   2篇
  2018年   1篇
  2017年   2篇
  2015年   3篇
  2014年   6篇
  2013年   22篇
  2012年   9篇
  2011年   16篇
  2010年   5篇
  2009年   4篇
  2008年   12篇
  2007年   11篇
  2006年   6篇
  2005年   7篇
  2004年   6篇
  2003年   6篇
  2002年   4篇
  2001年   3篇
  2000年   5篇
  1999年   1篇
  1998年   2篇
  1997年   6篇
  1996年   5篇
  1995年   3篇
  1994年   1篇
  1992年   3篇
  1990年   2篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   2篇
  1984年   2篇
  1982年   3篇
  1981年   2篇
  1977年   2篇
排序方式: 共有174条查询结果,搜索用时 15 毫秒
1.
We investigate the value of an optimal transportation problem with the maximization objective as a function of costs and vectors of production and consumption. The value is concave in production. For generic costs, the numbers of linearity domains and peak points are independent of costs and consumption. The peak points are determined by an auxiliary assignment problem. The volumes of the linearity domains are independent of costs while their dependence on consumption can be expressed via the multinomial distribution.  相似文献   
2.
In standard epistemic logic, the names and the existence of agents are usually assumed to be common knowledge implicitly. This is unreasonable for various applications in computer science and philosophy. Inspired by term-modal logic and assignment operators in dynamic logic, we introduce a lightweight modal predicate logic where names can be non-rigid, and the existence of agents can be uncertain. The language can handle various de dicto/de re distinctions in a natural way. We characterize the expressive power of our language, obtain complete axiomatisations of the logics over several classes of varying-domain/constant-domain epistemic models, and show their (un)decidability.  相似文献   
3.
The energy transfer from the upper triplet states of diphenylamine, naphthalene and triphenylene to toluene and hexene-1 is studed. Two mechanisms of dissipation transferred energy in solvents are discussed.  相似文献   
4.
This paper addresses scheduling models in which a contribution of an individual job to the objective function is represented by the product of its processing time and a certain positional weight. We review most of the known results in the area and demonstrate that a linear assignment algorithm as part of previously known solution procedures can be replaced by a faster matching algorithm that minimizes a linear form over permutations. Our approach reduces the running time of the resulting algorithms by up to two orders, and carries over to a wider range of models, with more general positional effects. Besides, the same approach works for the models with no prior history of study, e.g., parallel machine scheduling with deterioration and maintenance to minimize total flow time.  相似文献   
5.
We study a class of capacity acquisition and assignment problems with stochastic customer demands often found in operations planning contexts. In this setting, a supplier utilizes a set of distinct facilities to satisfy the demands of different customers or markets. Our model simultaneously assigns customers to each facility and determines the best capacity level to operate or install at each facility. We propose a branch-and-price solution approach for this new class of stochastic assignment and capacity planning problems. For problem instances in which capacity levels must fall between some pre-specified limits, we offer a tailored solution approach that reduces solution time by nearly 80% over an alternative approach using a combination of commercial nonlinear optimization solvers. We have also developed a heuristic solution approach that consistently provides optimal or near-optimal solutions, where solutions within 0.01% of optimality are found on average without requiring a nonlinear optimization solver.  相似文献   
6.
本文研究了在不同pH条件下P(AM/AA)溶液的13C-NMR谱,观察了谱峰的化学位移变化和分裂情况,对比了均聚物PAM和PAA的13C-NMR谱,对P(AM/AA)13C-NMR谱的各共振峰进行了归属,证实P(AM/AA)共聚物C=O碳峰的分裂只与分子链共聚序列结构相关,并得出了C=O碳分裂峰所对应的三单元序列结构。  相似文献   
7.
In this paper, we present several algorithms for the bi-objective assignment problem. The algorithms are based on the two phase method, which is a general technique to solve multi-objective combinatorial optimisation (MOCO) problems.  相似文献   
8.
In this work we consider scheduling problems where a sequence of assignments from products to machines – or from tasks to operators, or from workers to resources – has to be determined, with the goal of minimizing the costs (=money, manpower, and/or time) that are incurred by the interplay between those assignments. To account for the different practical requirements (e.g. few changes between different products/tasks on the same machine/operator, few production disruptions, or few changes of the same worker between different resources), we employ different objective functions that are all based on elementary combinatorial properties of the schedule matrix. We propose simple and efficient algorithms to solve the corresponding optimization problems, and provide hardness results where such algorithms most likely do not exist.  相似文献   
9.
10.
Abstract

Kinetic and equilibrium data for 1-EtIm binding to cyt c at temperature range of 303–319K have been determined at pH 7.0 by using 1HNMR method. Thermodynamic values (ΔH°=39.5 kJ mol?1, ΔS° = 154 J mol?1K?1 and Ea = 142 kJ mol?1) are obtained from Van't Hoff and Arrhenius's relations. Some hyperfine shifted resonances of l-EtIm cyt c have been assigned for the first time using 1D saturation transfer experiments. The origin of the asymmetric spin density distribution in heme groups of 1-EtIm cyt c and the reason of low affinity of cytochrome c for 1-EtIm are also discussed move toward upfield from original position. However, Te-2, 4 substituents in cyt c are more electron withdrawing than the propionic acid side chains, which lead to the 5-methyl group going toward downfield.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号